Many agencies now have stuck to outsourcing and this is the reason that it has become common to outsource guest posting. Today, there are many good writers outside and they are ready to write guest posts as they also get to earn their income.
There are advantages associated in doing so. It is simple to get in short time large numbers of guest posts and it allows the writers to create them in a short time. People also get to dictate and have complete control over the post content and its tone, without making it appear as a sale pitch alone.